An aspect of the present concepts relates to a method of controlling the pressing action between the parts to be joined. In vibration welding, melting of the plastic part interface is achieved when the parts are pressed together while one part vibrates relative to the other. The pressing action traditionally consists of applying either a constant force between the parts, or a force that varies based on a profile assigned prior to welding. This method of control has several limitations. First, the position of the first part in relation to the second part is not directly controlled, which reduces the accuracy and consistency of the collapsed height of the joined assembly. Second, the position of the first part relative to the second part cannot be statically maintained at some stages of the weld process, such as during the time after vibrations are halted but the plastic has not yet solidified, where the parts continue to move relative to each other due to the applied pressing force. Third, the speed of weld collapse is not directly controlled but is rather the result of the applied force and the dynamically changing compliance of the plastic parts. Benefits of overcoming the latter limitations, among other benefits, are set forth in the description of the present disclosure and as summarized below by way of a few non-limiting examples.
According to an aspect of the present disclosure, a vibration welding system is disclosed, where the operating vibration frequency is 260 Hz or higher.
According to another aspect of the present disclosure, a vibration welding system is disclosed, where the pressing action is effected by directly controlling, with a control system and at least one sensor, the relative position of the first workpiece to the second workpiece during some phase or the entirety of the weld cycle. The relative position of the workpieces can be maintained immediately after, or some time after, the vibrations are terminated.
According to a further aspect of the present disclosure, a vibration welding system is disclosed which includes an external control device coupled to the control system to produce at least one input signal to the control system to adjust the speed of relative motion between the first workpiece and the second workpiece, the force between the workpieces, or both speed and force on-the-fly based on an algorithm using said input signal.
According to yet another aspect of the present disclosure, a vibration welding system is disclosed in which the speed of collapse between the first workpiece and the second workpiece is independently programmable to be constant or variable during each of the various phases of the weld cycle, including melting and solidification.
According to a still further aspect of the present disclosure, a vibration welding system is disclosed where the pressing action between the first workpiece and the second workpiece is effected by controlling the speed between the workpieces during some phases of the weld cycle, and controlling the force between the workpieces during other phases of the weld cycle.
According to a further aspect of the present disclosure, a vibration welding system is disclosed in which a predetermined positive force is initially applied between the first workpiece and the second workpiece, and where the weld is started by initiating lateral vibrations while the relative position between the workpieces in the pressing direction is maintained, a control variable is monitored, and the second workpiece is moved relative to the first workpiece only after the monitored control variable satisfies a predetermined condition. The predetermined condition can be a specified force, or a specified power, or a specified cumulative power, or a specified voltage, or a specified current, or a specified cumulative current output from the vibration drive, and any quantity derived from the foregoing conditions. Alternately, the predetermined condition can be elapsed time. Alternately, the predetermined condition can be a sensed temperature of one or more areas of the workpieces being welded. Alternately, the predetermined condition can be a parameter associated with the actuating means of pressing the workpieces together, including the pressure of a fluid or pneumatic system, or the torque or linear force of an electric actuator. The amplitude of vibration, during the period when the relative position between the workpieces is maintained while vibrations are active, can be a fraction of the amplitude employed after subsequent pressing motion between the workpieces is initiated.
According to a still further aspect of the present disclosure, a vibration welding system is disclosed where the interface between the workpieces is pre-heated immediately before initiation of the weld process by operating the system at a reduced amplitude of vibration while the workpieces are urged together.
According to yet another aspect of the present disclosure, a vibration welding method is disclosed in which the operating vibration frequency is 260 Hz or higher.
According to an additional aspect of the present disclosure, a vibration welding method is disclosed in which first and second workpieces are pressed together by directly controlling the relative position of the first workpiece to the second workpiece. The relative position of the workpieces can be maintained immediately after, or some time after, the vibrations are terminated.
According to a still further aspect of the present disclosure, a vibration welding method is disclosed in which the speed of relative motion between a first workpiece and a second workpiece or the force between the workpieces is adjusted on-the-fly based on an algorithm in response to an input signal from an external control device coupled to the control system.
According to yet an additional aspect of the present disclosure, a vibration welding method is disclosed where the speed of collapse between the first workpiece and the second workpiece is constant or variable during each of the various phases of the weld cycle, including melting and solidification.
According to another aspect of the present disclosure, a vibration welding method is disclosed in which the pressing action between a first workpiece and a second workpiece is effected by controlling the speed between the workpieces during some phases of the weld cycle, and controlling the force between the workpieces during other phases of the weld cycle.
According to a further aspect of the present disclosure, a vibration welding method is disclosed in which a predetermined positive force is initially applied between a first workpiece and a second workpiece, and where the weld is started by initiating lateral vibrations while the relative position between the workpieces in the pressing direction is maintained, a control variable is monitored, and the second workpiece is moved relative to the first workpiece only after the monitored control variable satisfies a predetermined condition. The predetermined condition is a specified force, or a specified power, or a specified cumulative power, or a specified voltage, or a specified current, or a specified cumulative current output from the vibration drive. Alternately, the predetermined condition is elapsed time. Alternately, the predetermined condition is a sensed temperature of one or more areas of the workpieces being welded. Alternately, the predetermined condition is a sensed parameter associated with the actuating means of pressing the workpieces together, including the pressure of a fluid or pneumatic system, or the torque or linear force of an electric actuator. The amplitude of vibration, during the period when the relative position between the workpieces is maintained while vibrations are active, can be a fraction of the amplitude employed after subsequent pressing motion between the workpieces is initiated.
According to a still further aspect of the present disclosure, a vibration welding method is disclosed where the interface between the workpieces is pre-heated immediately before initiation of the weld process by employing a reduced amplitude of vibration while the workpieces are urged together.